Positively-driven, low tension transfer conveyor

ABSTRACT

Components of a conveyor system designed to facilitate tight transfer of products onto and off a positively-driven, low tension conveyor belt. The conveyor system includes a tension amplifier in a returnway of a conveyor belt circuit for selectively increasing tension in the conveyor belt prior to infeed without increasing the low tension in the returnway prior to the tension amplifier.

FIELD OF THE INVENTION

The present invention relates generally to power-driven conveyor belts,and more particularly to positively-driven, low tension conveyor beltsthat are driven as teeth engage sprockets or sprocket-like drivepulleys.

BACKGROUND OF THE INVENTION

Flat conveyor belting is traditionally configured to move through acircuit in a conveyor. The circuit includes a drive pulley, a carrywaytension zone, a returnway tension zone, an infeed and an outfeed. Inmany instances, the outfeed of the conveyor system also serves as thedrive pulley. In traditional configurations, the flat conveyor belt isdriven through the circuit by means of friction between the bottomsurface of the belt and the drive pulley. In order to create sufficientfriction to drive the belt along the circuit, the belt must bepre-tensioned.

FIG. 1 illustrates a conveyor 10 running a traditional, pretensioned,flat, friction-driven conveyor belt 60 suitable for transferringproducts to and from the conveyor. The conveyor includes a drive pulley30 below the conveyor 10, thereby enabling small diameter rollers in theinfeed 21 and the outfeed 22. Small diameter rollers in the infeed 21and outfeed 22 are desired when, for example, small product is desiredto transfer smoothly between conveyors.

As the flat, pretensioned, friction-driven, conveyor belt 60 moves inthe direction of arrow 62 from the infeed 21 to the drive pulley 30, itruns along a carryway tension zone 40, as distinguished from a returnwaytension zone 50, which extends from the drive pulley 30 to the infeed21.

The difference between the tension on the conveyor belt 60 at thebeginning of the returnway tension zone 50 and the tension on the belt60 at the end of the carryway tension zone 40 is referred to as the“tension differential,” and their ratio is referred to as the “tensionratio.” The maximum tension differential and the maximum tension ratiodepend upon the interplay between the coefficient of friction betweenthe drive pulley 30 and bottom surface of the conveyor belt 60 and thebelt arc of wrap in radians around the drive pulley 30. The maximumtension ratio can be calculated as follows:

$\frac{T_{CT}}{T_{RT}} = {\mathbb{e}}^{({{COF} \times {AW}})}$where T represents belt tension, T_(CT) represents the belt tension atthe end of the carryway tension zone 40, T_(RT) represents the belttension at the beginning of the returnway tension zone 50, COFrepresents the coefficient of friction between the bottom surface of thebelt 60 and the periphery of the drive pulley 30, and AW represents thearc wrap of the belt in radians.

In order for the conveyor belt 60 to drive through the circuit of theconveyor 10 of FIG. 1 with no product load, the conveyor belt 60 must bepretensioned. This pretension is referred to as static tension, asopposed to dynamic tension. Pretension is the tension in the conveyorbelt 60 that is applied prior to the operation of the conveyor belt.This static tension can be generated in different ways, but mostfrequently it is generated by extending the effective circuit lengthbeyond the natural length of the conveyor belt 60. The static pretensionis present in the conveyor belt prior to operation, when the belt isstationary, and also during operation. Even when product load is added,the predominant tension in the belt 60 is pretension. Therefore, theconveyor belt 60 has significant tension in the returnway tension zone50.

When product is conveyed along the carryway tension zone 40 of theconveyor 10, the load is increased and, with it, the tension on the beltin the carryway tension zone. As the belt returns through the returnwaytension zone 50 of the conveyor, the tension on the belt is reduced.

The maximum tension differential determines the amount of pretensionthat is required to effectively drive a flat conveyor belt for a givenmaximum amount of product load. When a flat conveyor belt is beingdriven without any product load, the actual tension differential will beat the lowest point. The tension on the belt in the returnway tensionzone will be similar to the tension on the belt in the carryway tensionzone. However, when product load is added, the actual tensiondifferential will increase. The higher the product load, the greater theactual tension differential will become. Therefore, since the maximumtension differential for a flat conveyor belt is limited by thepractical limits of arc of wrap and the coefficient of friction,pretension accounts for a significant portion of the tension in the beltat any given time, and in fact is often the majority of the tension inthe belt. The result is that when traditional flat conveyor belt isfriction driven, the belt experiences high amounts of tension throughoutthe length of the belt at all times.

An advantage of this inherently needed pretension is that, dependentupon the flexibility of the material construction of the belt, thefriction-driven belt can readily conform to various transitiongeometries at the infeed and outfeed of the conveyor.

However, there are two significant disadvantages to the inherentlyneeded pretension of a friction-driven, flat conveyor belt. The firstdisadvantage of using the high belt tensions is that misalignment of anycomponent in the conveyor causes large forces to off-track the belt,causing damage to both the conveyor and the belt.

A second disadvantage is that the flat conveyor belt 60 tends to stretchas pretension is applied. In order to limit the amount of stretch in theconveyor belt while maintaining flexibility, fabrics and cords are addedto restrict the stretch and enable the belt to operate under hightensions. However these fabrics and cords are a serious harborage pointof bacteria and possible pathogens in food processing applications. Thecommon off-tracking of the belt further causes edge fray promoting theexposed fabrics to wick foreign contaminates into the belt wherebacteria colonies can grow.

In recent years, a new style of conveyor belting has emerged to counterthese and other disadvantages of traditional flat conveyor belts. Forexample, a positively-driven, low-tension conveyor belt, such as theThermoDrive® belt available from Intralox, L.L.C., is driven throughpositive engagement of teeth on the bottom surface of the belt with asprocket or sprocket-like pulley, instead of pure friction. Apositively-driven conveyor belt has a dramatically higher maximumtension differential between the carryway tension zone and the returnwaytension zone and therefore the level of pretension is dramaticallyreduced. U.S. Pat. No. 7,850,562, entitled “Low Friction, Direct DriveConveyor Belt,” the contents of which are incorporated herein byreference, discloses a method under which such a belt can be driven withno pretension requirements at all. When utilizing the technologydescribed in U.S. Pat. No. 7,850,562, the tension ratio is theoreticallyinfinite. Yet even without this technology, the maximum tensiondifferential is significantly higher for positively-driven, low-tension,toothed conveyor belts than for traditional, friction-driven, flat,conveyor belting and thus the level of pretension required is low forpositively-driven conveyor belts.

There are two significant advantages of reducing pretension in apositively-driven conveyor belt. First, the tracking problems associatedwith misalignment in the conveyor are reduced or even removed. Further,because the pretension is so low, many belts are constructed with nofabric reinforcements at all, which improves food safety and hygiene infood processing applications.

An example of a flexible, endless, positively-driven, low tensionconveyor belt suitable for implementing an illustrative embodiment ofthe invention is shown in FIG. 2. An endless conveyor belt 160 in atypical installation moves around two cylindrical belt-guiding members,illustrated, as sprockets 112 and 114, through a circuit. A firstsprocket 114 may be a drive sprocket for driving the conveyor belt,while the second sprocket may be an idle, a driven or slave sprocket112. The drive sprocket 114 also functions as transition geometry in theoutfeed of the conveyor. The belt 160 has an outer surface 111 servingas an article-conveying surface and an inner surface 122 serving as adrive surface. The inner surface 122 includes drive elements,illustrated as teeth 126, preferably spaced equidistantly from eachother along the inner driven surface 122. The teeth 126 engage grooves116 spaced around the circumference of the sprockets 112, 114 to movethe belt. The upper span (carryway) 140 of the belt will travel in thedirection of arrow 115. The flexible belt 160 wraps around the sprocket114 and around one or more return rollers, or shoes or drums, in thereturn path (returnway). The conveyor belt 160 operates at low tension,resulting in substantial catenary sag (not shown) in the returnwaytension zone 150. The sprocket in the infeed 112 is of a larger diameterso that the positively-driven, toothed, low-tension, conveyor belt 160can properly conform to the sprocket in the infeed end of the conveyor.

The belt is made of a resilient material, such as a thermoplasticpolymer, an elastomer, or a rubber, and is flexible along its length.

To transfer products between two endless conveyor belts, the belts mustbe placed close together to minimize the gap between the conveyor beltsat the transfer point. Small nosebars, shoes or other structure areusually used at the transfer locations to allow the ends of the belts tobe placed in close proximity to each other.

A disadvantage of positively-driven, toothed, low tension, conveyorbelting is that without sufficient tension in the belt it does notreadily conform around transition points at the infeed that are smallerthan the arc of natural curvature in the belt as it transitions aroundthe infeed. Small transfers in ThermoDrive® and other low-tension,positive drive endless conveyor belts are often difficult, because thelack of tension prevents the belt from conforming to a small nosebar orother infeed structure.

FIG. 3A is a simplified schematic cross-sectional representation of aconveyor 200 running a positively-driven, toothed, low-tension, conveyorbelt 260, through a conveyor circuit in which small diameter cylindricalmembers are used at the infeed and outfeed. The conveyor circuitincludes a carryway 240 and a returnway 250. Smaller diameter sprockets211, 231 are used in the infeed 210 and outfeed 230 to facilitatetransfer of products onto and off the conveyor belt 260. However,problems arise when the sprocket 211 at the infeed 210 is smaller indiameter than the arc of the natural curvature of the belt 260 as ittransitions around the infeed 210, as shown in FIGS. 3A and 3B. Theresult of this smaller diameter sprocket in the infeed 210 is that theconveyor belt 260 protrudes beyond the plane of the belt circuitcreating a ridge 262 along the width of the conveyor belt 260 at theinfeed 210, which makes transfer of product onto the belt difficult.

To resolve these drawbacks, users of positively-driven, toothed,conveyor belting have resorted to adding more pretension than isrequired to drive the belt, in order to achieve the desired conformationaround the infeed roller, thus minimizing the tracking benefits andnon-fabric-reinforced sanitary benefits that could otherwise be achievedin a non-pretensioned belt.

The amount of pretension required to maintain belt conformity tospecific transition geometries at the infeed is greater than the amountof pretension required to achieve belt conformity at the infeed when thebelt is installed. This is because when product load is added and thetension differential increases, the added tension on the belt in thecarryway tension zone results in some amount of conveyor beltelongation. This additional belt length is generally found in thereturnway tension zone, resulting in a tension in the belt as itencounters the infeed that is lower than the pretension initiallyapplied. To maintain belt conformity around small transition geometriesat the infeed by means of pretension, the toothed, positively drivenconveyor belt will often be pretensioned beyond the pretension levelrequired to drive the conveyor belt.

SUMMARY OF THE INVENTION

The present invention provides a positively-driven, low tension conveyorsystem that facilitates transferring articles onto and off the conveyorbelt at the ends of the conveyor. The conveyor system includes a tensionamplifier to dynamically increase tension along a select portion of thebelt and may include a small infeed member, such as a rotatable, toothednosebar. The selective increased tension along only a portion of thebelt, preferably only while the belt is running, allows the belt toconform to the nosebar or other small infeed member of any geometry,facilitating transfers.

According to one aspect of the invention, a conveyor system comprises apositively-driven, low tension conveyor belt trained around belt-guidingmembers to form a circuit having a carryway, an infeed and a returnway.The conveyor system also includes a tension amplifier for increasingtension in a first section of the circuit, while the returnway of theconveyor belt prior to the tension amplifier remains substantiallyuntensioned.

According to another aspect, a method of conforming a positively-driven,low tension conveyor belt to an infeed member that is smaller than anatural arc of the conveyor belt is provided. The method comprises thesteps of running the conveyor belt through a circuit comprising acarryway having an infeed and an outfeed and a returnway below thecarryway, and increasing tension in the conveyor belt along a firstsection of the circuit using a tension amplifier without increasingtension along the returnway of the circuit prior to the tensionamplifier.

BRIEF DESCRIPTION OF THE FIGURES

These features of the invention, as well as its advantages, are betterunderstood by referring the following description, appended claims, andaccompanying drawings, in which:

FIG. 1 illustrates an endless flat conveyor belt of the prior art;

FIG. 2 is a simplified schematic cross-sectional representation of aconveyor running a positively-driven, toothed, low-tension, conveyorbelt of the prior art;

FIG. 3A is a simplified schematic cross-sectional representation of aprior art conveyor running a positively-driven, toothed, low-tension,conveyor belt in which the infeed section of the conveyor utilizes acylindrical member that is smaller in diameter than the arc of thenatural curvature of the belt;

FIG. 3B is an enlarged view of the cross-sectional representation of theridge along the width of the belt at the infeed shown in FIG. 3A;

FIG. 4 is a side view of a positively-driven, low tension conveyor beltsystem having a tension amplifier according to an illustrativeembodiment of the invention;

FIG. 5 is an isometric view of the positively-driven, low tensionconveyor belt system of FIG. 4 at an infeed end;

FIG. 6A is an isometric view of nosebar of the conveyor belt system ofFIGS. 4 and 5;

FIG. 6B is an end view of the nosebar of FIG. 6A;

FIG. 6C is a cross-sectional of the nosebar of FIG. 6A;

FIG. 7A illustrates a disc brake coupled to a set of sprockets in thereturnway of the conveyor of FIGS. 4 and 5;

FIG. 7B is a close-up view of the disc brake of FIG. 7A;

FIG. 7C is a front view of the disc brake and sprockets of FIG. 7A;

FIG. 8A is a schematic cross-sectional view of a positively-driven, lowtension conveyor belt system having tension amplifier according toanother embodiment of the invention;

FIG. 8B is an enlarged view of the tension amplifier of FIG. 8A.

FIG. 9A is a schematic cross-sectional view of a positively-driven, lowtension conveyor belt system having tension amplifier according toanother embodiment of the invention

FIG. 9B is an enlarged view of the tension amplifier of FIG. 9A;

FIG. 10 shows another embodiment of a tension amplifier suitable for usein a conveying system including a positively-driven, low tensionconveyor belt;

FIG. 11 shows another embodiment of a tension amplifier suitable for usein a conveying system including a positively-driven, low tensionconveyor belt;

FIG. 12A is a side view of an infeed portion of a conveyor systemincluding a tension amplifier according to another embodiment of theinvention;

FIG. 12B is an isometric view of the infeed portion of FIG. 12A;

FIG. 12C is an isometric view of the tension amplifier of FIG. 12B;

FIG. 12D is an exploded view of the tension amplifier of FIG. 12C; and

FIG. 13 is a chart showing the exponential growth of amplification dueto the increased arc of wrap of the conveyor belt under variouscoefficients of friction.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a system for facilitating transfer ofproducts to and from positively-driven, low tension endless conveyorbelts by dynamically increasing tension in a portion of the belt. Thepresent invention provides a tension amplifier and method fordynamically amplifying tension at a select and limited region of apositively-driven, low tension conveyor belt prior to the infeed of theconveyor to enable the conveyor belt to conform to an infeed member,such as a nosebar, roller, sprocket or shoe of any geometry, that issmaller than the natural curvature of the belt. The present inventionwill be described below relative to an illustrative embodiment. Thoseskilled in the art will appreciate that the present invention may beimplemented in a number of different applications and embodiments and isnot specifically limited in its application to the particularembodiments depicted herein.

FIGS. 4 and 5 illustrate a positively-driven, low tension conveyor beltsystem 300 having tight transfer geometry according to one embodiment ofthe invention. The conveyor belt system includes a tension amplifier forsufficiently amplifying tension in the returnway of the conveyor beltprior to the infeed to enable the belt to achieve a required transitionaround any geometry in the infeed, while simultaneously allowing thetension in the belt in the returnway zone prior to the point ofamplified tension to remain at low tension. The conveyor belt systemincludes a base 310 and a positively-driven, low tension conveyor belt360, such as the ThermoDrive® belt available from Intralox, L.L.C., theCleandrive positive drive belt available from Habasit AG, the GatesMectrol PosiClean® positive drive belt available from Gates Mectrol, theVolta SuperDrive™ and other positive drive belts available from VoltaBelting and other positively-driven, low tension conveyor belts known inthe art. The invention is not limited to these belts, and may beimplemented with any suitable positive-drive, low tension conveyor belt.The illustrative conveyor belt has a smooth outer surface substantiallyfree of discontinuities and an inner surface with a plurality of teethat a given belt pitch. The conveyor belt 360 conveys products along acarryway in the direction of arrow 363 and returns along a returnwaybelow the carryway. The conveyor belt may be conventionally trainedaround belt-guiding members, illustrated as driven sprockets 332 in thereturnway, drive sprockets 334 at the outfeed and a nosebar 350 at theinfeed of the carryway.

The first set of driven sprockets 332 is located in the returnway of theconveyor belt, and the second set of drive sprockets 334 is mounted atan end of the carryway for driving the conveyor belt. A passive, toothednosebar 350 is mounted at an end of the conveyor opposite the second setof sprockets. The nosebar 350 forms a guide structure for guiding theconveyor belt. In the illustrative embodiment, the nosebar is located atthe infeed end of the conveyor and the drive sprockets 334 are locatedat the discharge end of the conveyor.

The nosebar 350 is mounted on and is freely rotatable about a shaft 351connected to the base 310 at a first end. Roller bearings 354 facilitaterotation of the nosebar 350 about the shaft 351. The nosebar 350 has arelatively small diameter, smaller than the arc of the natural curvatureof the belt 360. The small radius of the nosebar allows a smaller gapbetween two conveyor belts or between the conveyor belt and anotherdevice.

A tension amplifier, illustrated as a braking device 380 coupled to thedriven sprockets 332 in the returnway, applies tension to the belt priorto infeed to allow the conveyor belt to wrap around the relativelysmall-diameter nosebar 350. A tension amplifier, such as a brakingdevice 380, allows the belt 360 to conform to the nosebar 350 in thetransfer region by applying select tension to only a portion of theconveyor belt 360, as described below. The braking device 380 of theillustrative embodiment is described below with respect to FIGS. 7A-7C.

Referring to FIGS. 6A-6C, the nosebar extends from a first end 353 to asecond end 354 and includes a plurality of teeth about its perimeter.The nosebar includes an axial opening 352 for receiving the shaft 351(shown in FIG. 4) about which the nosebar 350 rotates. The illustrativenosebar 350 includes five teeth 355 a-355 e, though the invention is notlimited to five teeth. Recesses 356 between the teeth receive driveelements on the drive surface of the conveyor belt 360. The illustrativeteeth 355 are larger than the recesses 356 and have curved edges.

In one embodiment, multiple nosebars may be mounted in series on a shaftwith braces therebetween.

Referring back to FIGS. 4 and 5, the conveyor system 300 furtherincludes a tension amplifier, illustrated as a braking device 380, fordynamically applying tension to select portions of the conveyor belt.The illustrative braking device 380 is a disc brake, shown in detail inFIGS. 7A-7C. The braking device may alternatively comprise a frictionbrake, hydraulic motor, electric motor, magnetic particle brake, weight,rollers or other suitable device. The braking device 380 allows the beltto conform to the small-diameter nosebar 350 or other belt-guidingmember. The braking device 380 dynamically increases tension in the beltto create a returnway amplified tension zone 322 in the conveyor beltcircuit, extending between the infeed end of the carryway 340 and thebraking device 380, to ensure that the belt wraps around the nosebar350. This increased tension remains in the conveyor belt 360 through thecarryway tension zone 340. The illustrative braking device 380 adds belttension through these zones to any tension that already exists in thebelt. As the belt transitions from the drive pulley 334 into thereturnway tension zone 345 the conveyor belt is relieved of thisdynamically inserted tension and is able to relax.

The braking device 380 is connected to a shaft 390 upon which the seriesof driven sprockets 332 are mounted. The illustrative braking devicecomprises a disc brake. The disc brake dynamically applies tension tothe returnway amplified tension zone 322 between the nosebar 350 and thedriven sprockets and through the carryway 340 by slowing the shaft 390to apply drag to the belt only in those regions, while the returnwaytension zone 345 remains under little to no tension.

The illustrative tension amplifier 380 dynamically increases tension inthe select portion of the belt circuit only when the drive sprockets aredriving the belt, causing the belt to move through the circuit. When theconveyor belt is stationary, the tension amplifier imparts no additionaltension. When the conveyor belt is stationary, only static tension,which is always present in the belt regardless of movement, such aspretension, is present in the belt and the tension amplifier 380 doesnot increase belt tension.

FIG. 8A illustrates a conveyor 400 having a positively driven, lowtension conveyor belt 460 and including a tension amplifier 480according to another embodiment of the invention. The conveyor 400 runsa positively-driven, toothed, low-tension, conveyor belt 460 through acircuit. The conveyor includes a small belt-guiding member 411, such asa sprocket, roller, nosebar, or static shoe at the infeed 410, a smallbelt-guiding member 421, such as a sprocket, roller, nosebar or staticshoe at the outfeed 420, a drive sprocket 430 below the carryway 440,and a tension amplifier 480 located in the returnway 450. The tensionamplifier creates a returnway amplified tension zone 490 between thecarryway tension zone 440 and the returnway tension zone 450 when theconveyor belt is running.

FIG. 8B is an enlarged view of the tension amplifier 480 in FIG. 8A. Thecylindrical member 411 at the infeed 410 is very small in diameter andthe conveyor belt 460 cannot naturally conform to the periphery of thesprocket at the infeed 410 with the low tension desired in the conveyorbelt 460 in the returnway tension zone 450. In the present invention,the tension amplifier 480 functions to multiply any tension alreadypresent in the conveyor belt 460 before the tension amplifier 480. Thetension amplifier creates a returnway amplified tension zone 490, whichis between the returnway tension zone 450, where the tension is requiredto be low, and the infeed 410, where the tension is required to besufficiently high to conform to the periphery of the small belt-guidingmember 411 in the infeed 410. The tension amplifier 480 dynamicallyincreases tension in the belt in the returnway amplified tension zone490 of the conveyor belt circuit, extending between the infeed end ofthe carryway 410 and the tension amplifier, to ensure that the beltwraps around the small belt-guiding member 411. This increased tensionremains in the conveyor belt 460 through the carryway tension zone 440.As the belt transitions from the drive pulley 430 into the returnwaytension zone 450, the conveyor belt is relieved of this dynamicallyincreased tension and is able to relax.

Preferably, the tension amplifier dynamically inserts tension into theselected portion of the belt circuit when the conveyor belt isoperating, adding no additional tension (static tension) to the conveyorbelt when the conveyor belt is stationary. Thus, when the conveyor beltis stationary, only static tension is present.

In one embodiment, the tension amplifier comprises one or morebelt-wrapping members, illustrated as rollers 470, 471, affixedperpendicular to the conveyor belt 460 within the circuit of the belt,preferably in the returnway. The rollers 470, 471 are parallel to eachother and separated by a selected distance. The drive surface 422 of theconveyor belt 460 rides along outer peripheries of the rollers 470, 471.Because the rollers 470, 471 are substantially resistant to therotational movement of the conveyor belt 460, drag is created in theconveyor belt 460. The drag created corresponds to the amount of arc ofwrap 480, 481 of the conveyor belt 460 around the rollers 470, 471.

The belt-wrapping members 470, 471 may have any suitable size, shape andform suitable for inducing drag in a conveyor belt that wraps around thebelt-wrapping member. In the illustrative embodiment, the belt-wrappingmembers are cylindrical rollers, but the belt-wrapping members mayalternatively have an elliptical shape, a semi-circular shape, apolygonal shape or any suitable geometric shape.

In one embodiment, optional wrap control rollers 440, 441 can bepositioned horizontally and vertically relative to the rollers 470, 471to alter the amount of wrap 480, 481 the conveyor belt 460 has aroundthe rollers 470, 471, thereby controlling the amount of drag created inthe amplified tension zone 490.

In another embodiment, not shown in FIG. 8B, the substantiallycylindrical rollers 470, 471 may be substantially fixed by use of anexternal brake. The external brake may function as a safety clutch thatenables the substantially fixed rollers 470, 471 to selectively rotatewhen the tension required to conform the belt to the geometry at theinfeed 410 is exceeded. The clutch releases the rollers 470, 471 if themultiplied tension is too high, given the levels of incoming tension.

In yet another embodiment, not shown in FIG. 8B, the substantially beltwrapping members 470, 471 may include recesses or other geometry forengaging the teeth of the conveyor belt 460.

In one embodiment, the wrap control rollers 440, 441 rotate along withthe conveyor belt 460.

In another embodiment, the wrap control rollers 440, 441 are fixed andresist the rotational movement of the conveyor belt 460 thereby creatingdrag with the surface of the conveyor belt 460 regardless of the profileof the belt surface.

A sensor or other device may monitor the tension amplifier 480 and-orthe tension in the conveyor belt 460 between the amplifier 480 and theinfeed 410. The sensor may be connected to a controller for controllingthe positions of the rollers 470, 471 to alter the effective arc of wrapin order to achieve the desired tension in the positively-drivenconveyor belt in the amplified tension zone 490 between the tensionamplifier 480 and the infeed 410.

FIG. 9A is a simplified schematic cross-sectional representation of aconveyor 500 running a positively-driven, toothed, low-tension, conveyorbelt 560, with a belt-guiding member 511, such as a sprocket, roller,nosebar or static shoe, at the infeed 510 and a tension amplifier 580disposed in the returnway 550 of the belt. The conveyor also includes asmall belt-guiding member 521, such as a sprocket, roller, nosebar orstatic shoe, at the outfeed 520 and a drive sprocket 530 below thecarryway 540. The tension amplifier 580 creates a returnway amplifiedtension zone 590 when the conveyor belt is running by multiplyingtension already in the belt prior to the tension amplifier. Thereturnway amplified tension zone 590 created by the tension amplifierextends between the carryway tension zone 540 and the returnway tensionzone 550. The tension amplifier 580 comprises a serpentine arrangementof substantially fixed, belt-wrapping members, illustrated as rollers572, 573, 574, 575, inserted into the belt circuit, preferably in thereturnway. The conveyor belt 560 serpentines through the rollers 572,57, 574, 575 to provide resistance and increase tension in the zone 590by multiplying the tension already in the belt as it enters the tensionamplifier 580. This increased tension remains in the conveyor belt 560through the carryway tension zone 540. As the belt transitions from thedrive pulley 530 into the returnway tension zone 550, the conveyor beltis relieved of this dynamically increased tension and is able to relax.

FIG. 9B is an enlarged view of the tension amplifier 580 of FIG. 9A. Inone embodiment, the arc of the wrap 582, 583, 584, 585 of the beltaround the rollers is determined by the proximity of the two or morebelt-wrapping members 572, 573, 574, 575 relative to each other.

In one embodiment, the belt-wrapping members 572, 573, 574, 575 can beadjusted relative to each other based upon a measurement of the tensionbeing generated by the tension amplifier 580. A sensor or other devicemay measure the tension and send signals to a controller that controlsthe separation distance or position of the substantially cylindricalobjects 572, 573, 574, 575 in order to control the amount of tension inthe conveyor belt through the amplified tension zone 590.

While the illustrative belt-wrapping members comprise substantiallycylindrical rollers, the belt wrapping members in the tension amplifier580 may have any suitable geometry for multiplying tension in a conveyorbelt.

FIG. 10 is a simplified schematic cross-sectional representation ofanother embodiment of the dynamic tension amplifier of FIG. 9B, in whichthe belt-wrapping members, illustrated as substantially cylindricalobjects 572′, 573′, 574′, 575′, for wrapping a positively-driven, lowtension conveyor belt 560′ are in closer horizontal proximity than inFIG. 9B, resulting in a greater arc of wrap 586′, 587′, 588′, 589′.

FIG. 11 illustrates another embodiment of a positively-driven, lowtension conveyor belt conveying system 600 including a tension amplifieraccording to another embodiment of the invention. The tension amplifier680 of FIG. 11 comprises a plate or rail system. The plate or railsystem comprises an upper member 681, comprising a plate or rail,disposed adjacent to the drive surface of the conveyor belt 660 in thereturnway and a lower member 682, comprising one or more rails adjacentto the conveying surface of the conveying belt in the returnway. Theconveyor belt runs between the members 681, 682 under adjustable levelsof pressure, thereby inducing drag on the conveyor belt to selectivelyadd dynamic tension to the belt. In one embodiment, the rails may bev-shaped or otherwise shaped in the direction of the drive and therebyalso serve as a scraper to clean the belt. The dynamic tension creates atension amplified zone 690 prior to the infeed 611. The increasedtension remains in the belt through the carryway tension zone 640 to thedrive pulley 630. As the belt transitions from the drive pulley 630 intothe returnway tension zone 650, the conveyor belt 660 is relieved ofthis dynamically increased tension and is able to relax.

FIG. 12A-12D illustrates a tension amplifier 780 for a positivelydriven, low tension conveyor belt 760 according to another embodiment ofthe invention. The conveyor 700 runs a positively-driven, toothed,low-tension, conveyor belt 760 through a circuit. The conveyor includesa small belt-guiding member 711, such as a sprocket, roller, nosebar, orstatic shoe at the infeed 710, and a tension amplifier 780 located inthe returnway 750. A drive sprocket (not shown) is located at anotherlocation in the circuit. The tension amplifier creates a returnwayamplified tension zone 790 between the carryway tension zone 740 and thereturnway tension zone 750 when the conveyor belt is running to help thebelt 760 conform to the infeed belt-guiding member 711.

The tension amplifier includes a frame 781 for mounting the variouscomponents of the tension amplifier to the conveyor. The frame 781comprises two opposing plates 782 connected by support beams 784. Thesupport beams 784 extend along the length and width of the frame. Thetension amplifier includes a plurality of belt-wrapping members, shownas rollers 770 and 771, are mounted to the frame 781 within thereturnway of the belt. The drive surface of the conveyor belt 760 ridesalong outer peripheries of the rollers 770, 771. The side plates 782include openings 783 for mounting the rollers 770, 771.

In the illustrative embodiment, each roller 770, 771 comprises acylindrical member 772 having triangular mounting tabs 775 extendinglongitudinally along the top of the cylindrical member. The cylindricalmember 772 is inserted in a sleeve 773 having a longitudinally extendingprotrusion 776 including a triangular opening for receiving thetriangular mounting tabs 775. The openings 783 in the side plates 782include square recesses for receiving the protrusions on the sleeve,preventing rotation of the rollers when mounted.

The belt-wrapping members 770, 771 may have any suitable size, shape andform suitable for inducing drag in a conveyor belt that wraps around thebelt-wrapping member. In the illustrative embodiment, the belt-wrappingmembers are cylindrical rollers with protrusions, but the belt-wrappingmembers may alternatively have an elliptical shape, a semi-circularshape, a polygonal shape or any suitable geometric shape.

In one embodiment, optional wrap control rollers 740, 741, 742, 743 canbe positioned relative to the rollers 770, 771 to control the amount ofwrap the conveyor belt 760 has around the rollers 770, 771, therebycontrolling the amount of drag created in the amplified tension zone790. The position of the inside wrap control rollers 741, 742 may bevariable to allow for adjustment to the amount of wrap.

As shown, the top of each side plate 782 includes two sets of slots 787,788 extending at angles. An inside wrap control roller 741, 742 isinserted into a slot from each set. The position of each inside wraproller is adjustable. As shown in FIG. 12D, each wrap control roller741, 742 includes an end cap 743 with flat sides configured to bereceived in a slot. The configuration of the end cap 743 and slotsprevent rotation of the wrap control rollers when inserted.

The side plates 782 also include outer slots 789 a, 789 b for mountingthe outer wrap rollers 740, 743.

FIG. 13 is a chart showing the exponential growth of amplification dueto the increased arc of wrap of the conveyor belt under variouscoefficients of friction. As shown, the tension amplification ratiogenerally increases with the effective arc of wrap of the conveyor beltaround a cylindrical member.

The use of a tension amplifier in the returnway of a positively-driven,low tension conveyor belt allows the conveyor belt to conform to amember at an end of the conveyor belt that is smaller than the naturalarc of curvature of the conveyor belt by increasing tension in only aportion of the conveyor belt circuit. The ability to only increasetension in the selected zone while the conveyor belt is running, withoutincreasing tension when the conveyor belt is stationary, reduces wear,increases the life of the conveyor belt and improves tracking. Anysuitable means for selectively and dynamically increasing tension in alimited portion of a conveyor belt circuit without increasing thenear-zero tension of the conveyor belt in the returnway tension zoneprior to the tension amplifier may be used.

The scope of the claims is not meant to be limited to the details of thedescribed exemplary embodiments.

What is claimed is:
 1. A conveyor system, comprising: apositively-driven, low tension conveyor belt trained around belt-guidingmembers to form a circuit having a carryway, an outfeed and a returnway;and a tension amplifier located in the returnway for increasing tensionin a first section of the circuit between the tension amplifier and thecarryway, while the returnway of the conveyor belt between the outfeedand the tension amplifier remains substantially untensioned.
 2. Theconveyor system of claim 1, wherein the tension amplifier comprises abrake connected to a sprocket in the returnway of the circuit.
 3. Theconveyor system of claim 1, further comprising a passive toothed nosebarat the infeed of the circuit.
 4. The conveyor system of claim 1, furthercomprising a sensor for monitoring tension in the conveyor belt afterthe tension amplifier and a controller for adjusting the tensionamplifier based on the monitored tension.
 5. The conveyor system ofclaim 1, wherein the tension amplifier comprises a rail adjacent to aconveying surface of the conveying belt and an opposing plate or railadjacent to a drive surface of the conveyor belt for adding drag to theconveyor belt.
 6. The conveyor system of claim 5, wherein the railadjacent to the conveying surface is v-shaped.
 7. The conveyor system ofclaim 1, wherein the tension amplifier comprises a plurality ofbelt-wrapping members disposed in the returnway and perpendicular to thecircuit.
 8. The conveyor system of claim 7, wherein the conveyor beltwraps around the belt-wrapping members to induce drag in the conveyorbelt.
 9. The conveyor system of claim 7, further comprising a frame formounting the belt-wrapping members.
 10. The conveyor system of claim 9,wherein the frame includes a plurality of slots for adjusting theposition of at least one of the belt-wrapping members.
 11. The conveyorsystem of claim 7, wherein the belt-wrapping members are substantiallyresistant to rotational movement.
 12. The conveyor system of claim 11,wherein the belt-wrapping members are fixed to prevent rotationalmovement.
 13. The conveyor system of claim 11, further comprising abrake for causing the belt-wrapping members to resist rotationalmovement.
 14. The conveyor system of claim 13, wherein the brakefunctions as a safety clutch that enables the belt-wrapping members torotate when the tension required to conform the conveyor belt to aninfeed member is exceeded.
 15. A method of conforming apositively-driven, low tension conveyor belt to an infeed member that issmaller than a natural arc of the conveyor belt, comprising the stepsof: running the conveyor belt through a circuit comprising a carrywayhaving an infeed and an outfeed, and a returnway below the carryway; andincreasing tension in the conveyor belt along a first section of thecircuit using a tension amplifier in the returnway without increasingtension along the returnway of the circuit prior to the tensionamplifier; and releasing the tension added by the tension amplifier atthe outfeed, so that a second section of the circuit between the outfeedand the tension amplifier remains substantially untensioned.
 16. Themethod of claim 15, wherein the tension amplifier comprises a brakeconnected to a shaft upon which driven sprockets are mounted in thereturnway.
 17. The method of claim 15, further comprising the steps of:monitoring the tension in the first section; and adjusting the tensionamplifier based on the step of monitoring.
 18. The method of claim 15,wherein the tension amplifier comprises a rail system in the returnway.19. The method of claim 15, wherein the tension amplifier comprises aseries of belt-wrapping members disposed in the returnway andperpendicular to the circuit.
 20. The method of claim 19, wherein thebelt-wrapping members are substantially resistant to rotationalmovement.
 21. The method of claim 19, further comprising the step ofbraking the belt-wrapping members to resist rotational movement.
 22. Themethod of claim 21, further comprising the step of allowing thebelt-wrapping members to rotate when the tension in the conveyor beltexceeds a select amount.
 23. A conveyor system, comprising: apositively-driven, low tension conveyor belt trained around an infeedbelt-guiding member and an outfeed belt-guiding member to form a circuithaving an infeed, a carryway, an outfeed and a returnway below thecarryway; and a tension amplifier disposed in the returnway fordynamically increasing tension in a first section of the circuit betweenthe tension amplifier and the infeed without adding static tension tothe conveyor belt, while the returnway of the conveyor belt between thetension amplifier and the outfeed remains substantially untensioned. 24.The conveyor system of claim 23, wherein the infeed belt-guiding memberhas a diameter that is less than the arc of natural curvature of theconveyor belt.